Aspect Ratio Patterns Research Articles

High-temperature atomic layer deposition of silicon oxide films using Tris(dimethylamino)silane and ozone

Atomic layer deposition (ALD) benefits from high process temperatures when the substrate is not temperature-sensitive because the films deposited at higher temperatures exhibit better electrical properties. In this study, we investigated the ALD process of silicon oxide films by alternating injections of tris(dimethylamino)silane (tris-DMAS) and O3/O2 at temperatures ranging from 400 to 700 °C. The saturation dose of tris-DMAS was 1.5 × 106 L at 400 °C. Self-limiting growth with a growth rate of approximately 0.9 Å/cycle was observed up to 600 °C, allowing excellent step coverage. However, at 700 °C, the growth rate increased significantly to 4.6 Å/cycle, carbon and nitrogen impurities were detected by secondary ion mass spectrometry, and step coverage was poor, supporting the thermal decomposition of tris-DMAS at this temperature. Therefore, the optimum temperature for ALD SiO2 using tris-DMAS is 600 °C for application as an insulating film on high aspect ratio patterns. At this temperature, the leakage current density was 0.58 nA/cm2, and the oxide-trapped charge density was 4.0 × 1010 cm−2.

Si-Containing Reverse-Gradient Block Copolymer for Inorganic Pattern Amplification in EUV Lithography.

Although extreme ultraviolet lithography (EUVL) has emerged as a leading technology for achieving high quality sub-10 nm patterns, the insufficient pattern height of photoresist patterns remains a challenge. Directed self-assembly (DSA) of block copolymers (BCPs) is expected to be a complementary technology for EUVL due to its ability to form periodic nanostructures. However, for a combination with EUV patterns, it is essential to develop advanced BCP systems that are suited to inorganic-containing EUV photoresists and offer improved resolution limits, pattern quality, and etch resistance. Here, we report a reverse-gradient BCP system, poly[(styrene-gradient-pentafluorostyrene)-b-4-tert-butyldimetilsiloxystyrene] [P(S-g-PFS)-b-P4BDSS] BCP, which enables universally vertically oriented lamellae even in the absence of a neutral layer, while also containing a Si-containing block with high etch resistance. The gradient block, characterized by a gradual compositional transition from the block junction to the tail, plays a crucial role in creating an adequate surface energy contrast that energetically drives the formation of perpendicular lamellae without neutral layer. When used as a pattern height enhancement layer in EUVL, a high aspect ratio (3.29) of patterns was achieved, thereby offering a supplementary solution for next-generation EUVL.

Efficiency of high energy fluorocarbon molecule bombardment for fast etch rate and its limitation: A molecular dynamics study

The RF power of the High Aspect Ratio (HAR) patterning equipment used for 3D NAND memory etching processes rapidly increased recently. However, despite implementing higher ion energy, its effect on increasing the etch rate is not satisfactory. This letter studies the energy transfer efficiency between bombarding fluorocarbon (FC) molecules and the SiO2 substrate, and discusses the limitation of securing the etch rate by high-energy FC molecules.

Development of stimuli-responsive flexible micropillar composites via magneto-induced injection molding and characterization of magnetic particle alignment

Magnetic soft composites have emerged as a promising soft actuator with a high degree of precision in the magnetic field stimuli system. But, their mass manufacturing strategies have yet to be developed, and most studies focus on small-scale near-net shaping production. Here, we first apply injection molding (which only takes a few seconds to shape) to fabricate the stimuli-responsive flexible micropillar composites with magnetic particle alignment design using an external magnetic field. The arrays exhibit magnetically anisotropic particle alignment up to 82.57 % along the longitudinal direction, showing a magnetic bending actuation response. We achieve a structural novelty of the magnetic micropillar with a high aspect ratio of up to 10 and pattern sizes of 50 μm via sacrificial LIGA insert mold and magneto-induced injection molding. For advanced mass production, the permanent metal mold is also applied to develop the micropillar composites based on the mechanical demolding approach; successful manufacturing is achieved by fabricating defect-free micropillar with 200 μm cylindrical pattern size and aspect ratio of 6. Further, the effect of powder volume fraction on the magneto-rheological behavior and corresponding magnetic performance is characterized in the injection molding process. The magnetic particle alignment trend is confirmed by the torque balance and the criteria of critical solids loading. Finally, we establish an injection molding process for magnetic soft composites, and verify the optimal powder fraction for the particle alignment.

Modification of Turing patterns through the use of time-varying anisotropic diffusion

The Turing mechanism underpinning pattern formation in reaction–diffusion relies on the interplay between diffusion parameters and reaction kinetics. Diffusion is typically assumed isotropic, however anisotropic diffusion is known to arise in both nature and laboratory conditions. We study how the Turing instability and resulting Turing patterns are modified when the underlying diffusion tensor is both anisotropic and time-dependent, modelling, for instance, chemical species reacting and diffusing through time-varying anisotropic media. We show that the set of unstable wavenumber vectors corresponding to Turing modes evolve in a spatially biased manner under this anisotropy, thereby modifying the spatial scale and structure of any resulting Turing patterns differently along each spatial coordinate. We employ this spatial bias to develop control strategies to modify the shape or even structure of Turing patterns over time. We are able to make minor changes to the aspect ratio of Turing patterns, such as morphing circular Schnakenberg spots into elliptical spots, as well as more major changes to the structure of patterns, for instance converting Gierer–Meinhardt spots into stripes or FitzHugh–Nagumo labyrinthine patterns into target patterns. Our results suggest that time-varying anisotropic media may be used as a tool by which to modify and even control Turing patterns.

Controlling the Morphological Features, Aspect Ratio and Emission Patterns of Supramolecular Copolymers by Restricted Dimensional Growth.

One of the bottlenecks associated with supramolecular polymerization of functional π-systems is the spontaneous assembly of monomers leading to one- or two-dimensional (1D or 2D) polymers without control over chain length and optical properties. In the case of supramolecular copolymerization of monomers that are structurally too diverse, preferential self-sorting occurs unless they are closely interacting donor-acceptor pairs. Herein, it is established that the spontaneous 1D polymerization of a phenyleneethynylene (PE) derivative and the 2D polymerization of a Bodipy derivative (BODIPY) can be controlled by copolymerizing them in different ratios, leading to unusual spindle-shaped structures with controlled aspect ratio, as evident by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) studies. For example, when the content of BODIPY is 50 % in the BODIPY-PE mixture, the 1D polymerization of PE is significantly restricted to form elongated spindle-like structures having an aspect ratio of 4-6. The addition of 75 % of BODIPY to PE resulted in circular spindles having an aspect ratio of 1-2.5, thereby completely restricting the 1D polymerization of PE monomers. Moreover, the resultant supramolecular copolymers exhibited morphology and aspect ratio dependent emission features as observed by the time-resolved emission studies.

Negative Photo-Definable Polyimide Dry Films for Fine and High Aspect Ratio Patterning

We newly developed a negative photo-definable polyimide dry films with higher photoreactivity than conventional ones. We succeeded in fine and high aspect ratio patterning with 90 μm thickness and 8 μm width by using new polyimide dry films. When compared after curing, the tensile breaking strength and share strength of new and conventional polyimide dry films were almost the same. However, when compared after PEB and exposure, the new ones showed clearly higher properties than conventional one. Using this polyimide dry film as an inter-layer dielectrics or a permanent resist was effective in improving the wiring density of electric devices.

Effect of pH and Ion Concentration on Wetting of Nanoholes and Water Structuring

Like supervias in the back end of line, and deep contact holes with an aspect ratio higher than sixty in 3D-NAND memory, higher aspect ratio patterning is one of the important issue in advanced semiconductor manufacturing. As with the difficulty of patterning, the technique of cleaning the nanostructure so that it does not affect the next process is also considered important. In semiconductor cleaning, chemicals such as HF and NH4OH that include reactant ions are used for cleaning the semiconductor surface. Ions in bulk aqueous solutions were shown either as structure making or breaking effects in Marcus’s study (Chem. Rev., 2009). The classification of ions as structure making or breaking was confirmed using 1 M solutions in nanotrenches (Vereecke, Micro. Eng., 2021). This shows there is an ion effect, and it can change properties between solution and material surface. The addition of structure breaking ions in HF solutions was used to decrease the etch rate of oxide between fins (Vereecke, Micro. Eng., 2022). Going further from Marcus’s study, we focused on pH and ion concentration in the addition of structure making ions. In the nanostructure, it was considered necessary to study because the surface properties may vary depending on the degree of structuring and the influence of the zeta potential depending on the concentration and pH of the ions.In this work, we used an in-situ ATR-FTIR (Attenuated Total Reflection – Fourier Transformed Infra-Red) spectroscopy technique (Nicolet iS50 AEM, Thermo Fisher Scientific, USA) to characterize the wetting of nanostructures embedded in a silica matrix by UPW (Ultra-Pure Water) and electrolyte solutions, and a streaming zeta potential analyzer (SURPASS3, Anton Paar, Austria) to characterize the surface potential of flat surfaces of the same material. Wetting in the nanostructures was characterized by an analysis of the ratio of the OH stretching peak to OH bending peak (Vrancken, Langmuir, 2016). Also, dissolution of CO2 in the wetted nanostructures was monitored to compare the solubility and diffusivity in the nano-confined solutions with that in bulk solutions. In this experiment, we used dense arrays of silicon nanoholes in a PEALD SiO2 matrix (depth of about 300 nm, diameter of about 20 nm, and pitch 90 nm) that were fabricated on Si wafers using arrays of nanostructures, as described in Vereecke (2021). Crystal drying, wetting with a solution, and applying CO2 were performed in this order. HI, HBr, HCl were used for chemicals and pH 1, 2, 3, 4 was used for pH.Monitoring of the OH stretching to bending ratio showed little improvement in wetting as a function of pH between 1 to 4 as compared to UPW. Also, little difference was observed when changing the acid from HCl to HBr and HI, with anions of higher structure breaking properties according to Marcus (Chem. Rev., 2009). A higher CO2 solubility and a lower CO2 diffusivity were measured in the nanoconfined solutions as compared to bulk UPW, indicative of water structuring. A higher CO2 solubility at pHs 2-3 as opposed to pH 1 and 4 may originate from the proximity to the isoelectric point. Results will be complemented with tests performed at the isoelectric point and pH 0, with 1 M solutions where structure breaking properties of the used anions are expected to be stronger and wetting might be improved.

Tailoring an Interface Microstructure for High-Performance Reversible Protonic Ceramic Electrochemical Cells via Soft Lithography.

Micropatterning is considered a promising strategy for improving the performance of electrochemical devices. However, micropatterning on ceramic is limited by its mechanically fragile properties. This paper reports a novel imprinting-assisted transfer technique to fabricate an interlayer structure in a protonic ceramic electrochemical cell with a micropatterned electrolyte. A dense proton-conducting electrolyte, BaCe0.7Zr0.1Y0.1Yb0.1O3-δ, is micropatterned in a chevron shape with the highest aspect ratio of patterns in electrode-supported cells to the best of our knowledge, increasing surface areas of both electrode sides more than 40%. The distribution of relaxation time analysis reveals that the chevron-patterned electrolyte layer significantly increases the electrode contact areas and active electrochemical reaction sites at the vicinity of the interfaces, contributing to enhanced performances of both the fuel cell and electrolysis operations. The patterned cell demonstrates improved fuel cell performance (>45%) and enhances electrolysis cell performance (30%) at 500 °C. This novel micropatterning technique is promising for the facile production of layered electrochemical cells, further opening a new route for the performance enhancement of ceramic-based electrochemical cells.

Effect of pH and Ion Concentration on Wetting of Nanoholes and Water Structuring

In advanced semiconductor manufacturing, with deep contact holes with an aspect ratio higher than sixty in 3D-NAND memory, higher aspect ratio patterning is one of the important issues in advanced semiconductor manufacturing. In this work, we used an in-situ ATR-FTIR spectroscopy technique to characterize the wetting of nanostructures embedded in a silica matrix by UPW and electrolyte solutions as a function of pH. There was little influence of pH on the wetting of nanoholes in the studied range of 1 to 4, but wetting seemed to be less close to the isoelectric point. Also, HCl seemed to lend a better wetting compared to HI, in opposition to their structure breaking effect according to Marcus. A correlation was observed between these observations and the CO2 solubility, indicative of the influence of water structuring.

Sequential Infiltration Synthesis into Maltoheptaose and Poly(styrene): Implications for Sub-10 nm Pattern Transfer.

Vapor phase infiltration into a self-assembled block copolymer (BCP) to create a hybrid material in one of the constituent blocks can enhance the etch selectivity for pattern transfer. Multiple pulse infiltration into carbohydrate-based high-χ BCP has previously been shown to enable sub-10 nm feature pattern transfer. By optimizing the amount of infiltrated material, the etch selectivity should be further improved. Here, an investigation of semi-static sequential infiltration synthesis of trimethyl aluminum (TMA) and water into maltoheptaose (MH) films, and into hydroxyl-terminated poly(styrene) (PS-OH) films, was performed, by varying the process parameters temperature, precursor pulse duration, and precursor exposure length. It was found that, by decreasing the exposure time from 100 to 20 s, the volumetric percentage on included pure Al2O3 in MH could be increased from 2 to 40 vol% at the expense of a decreased infiltration depth. Furthermore, the degree of infiltration was minimally affected by temperature between 64 and 100 °C. Shorter precursor pulse durations of 10 ms TMA and 5 ms water, as well as longer precursor pulses of 75 ms TMA and 45 ms water, were both shown to promote a higher degree, 40 vol%, of infiltrated alumina in MH. As proof of concept, 12 nm pitch pattern transfer into silicon was demonstrated using the method and can be concluded to be one of few studies showing pattern transfer at such small pitch. These results are expected to be of use for further understanding of the mechanisms involved in sequential infiltration synthesis of TMA/water into MH, and for further optimization of carbohydrate-based etch masks for sub-10 nm pattern transfer. Enabling techniques for high aspect ratio pattern transfer at the single nanometer scale could be of high interest, e.g., in the high-end transistor industry.

High-integration and high-performance micro thermoelectric generator by femtosecond laser direct writing for self-powered IoT devices

Astonishing advances in IoT devices are making a revolutionary progress on smart society, but requiring for sustainable micro power sources. Micro thermoelectric generators (μTEGs) have the potential to power the IoT devices when incorporated into compact microcircuits. Nevertheless, the relatively low output of μTEGs can hardly reach the rated power and voltage for practical use at present. Herein, a femtosecond laser direct writing method is proposed for the fabrication of μTEGs with easy operation and good compatibility, and the precise adjustment of laser energy ensures a high-precision high aspect ratio pattern etch of thermoelectric films. The highly-integrated μTEG (364 pairs/cm2) meets an excellent output of 494 mV and 0.514 mW cm−2 at ΔT = 33.1 K and an efficiency factor of 0.47 μW cm−2 K−2. Eventually, it can realize an output of 3.3 V by using a power manager with the function of stabilizing and drive various electronic components, exhibiting a promising power source for self-powered IoT devices.

Percolation threshold and effective properties of CNTs-reinforced two-phase composite materials

In this paper an analytical prediction model is developed to determine the percolation threshold and effective properties of carbon nanotubes reinforced two-phase composite materials. The model considers the effect of not only volume fraction but also aspect ratio and mixed pattern of fibres in the composites. It is shown that the effect of fibres on the effective properties of the composites can be characterised in terms of three different zones, namely non-percolated zone, partially percolated zone, and fully percolated zone. The formulations for determining percolation threshold and effective properties of the composites in the three different zones are derived. The model is validated by using available experimental data to demonstrate its appropriateness and reliability.

Free vibrational characteristics of GNP-reinforced joined conical–conical​ shells with different boundary conditions

The current study is devoted to analyzing the free vibration characteristics of joined conical–conical shells made of epoxy enriched with graphene nanoplatelets (GNPs). The mathematical modeling of the shell is performed utilizing the first-order shear deformation theory (FSDT) to incorporate the effects of shear deformations and rotational inertia. The effective modulus of elasticity is estimated using the Halpin–Tsai model and other effective mechanical properties are evaluated utilizing the rule of mixture. The set of the governing equations, associated compatibility conditions at the intersection of two shell segments, and boundary conditions are obtained using Hamilton’s principle. These equations are solved in the circumferential direction using trigonometric functions and a numerical solution is provided in the meridional direction utilizing the differential quadrature method (DQM). Through this semi-analytical solution, the natural frequencies of the shell and corresponding mode shapes are determined and the validity of the presented solution is confirmed via the benchmark results reported by the other authors. The effects of various parameters on the natural frequencies of the GNP-reinforced joined conical–conical​ shells are examined including the circumferential wave number, the boundary conditions, the length-to-small radius ratio and semi-vertex angle in two shell segments, thickness-to-small radius ratio of the shell, and also mass fraction, aspect ratio, and dispersion pattern of the GNPs.

Direct visualization of beam-resist interaction volume for sub-nanometer helium ion beam-lithography

Interaction volume of beam-resist is a basis unit of beam-lithography, directly determines the critical parameters of beam-lithography. We have visualized the interaction volume at the state-of-the-art sub-10 nm scale by a spot irradiation of sub-nanometer helium ion beam into an approximately free-standing resist. The visualized interaction volume suggests helium ion beam has an excellent capability in nanofabrication. Specifically, helium ion beam-lithography is 1000 times more efficient than electron beam-lithography (EBL), owns a sub-4 nm resolution, can achieve a large pattern aspect ratio (greater than 8), and does not suffer from backscattering effect at a normal exposure dose. Furthermore, the interaction volume has been theoretically studied by considering the spatial distribution of energy deposited in the resist, and eventually lead to a model for pattern prediction and proximity effect corrections. We expect that, our approach to visualize the interaction volume may be applied to study other high resolution lithographic techniques such as x-ray lithography and EBL, and it may open new possibilities in other applications, like beam-imaging, beam-milling, and beam-modification.

Control of dielectric properties of micropattern printed fabric for radar absorbing structures

Recently, research has been carried out on radar absorbing structures (RASs) that simultaneously perform structural functions and provide low observability. The method of imparting conductivity by mixing a resin with conductive particles, such as carbon nanotubes, has been utilized since the early stages of RASs. This is advantageous because it enables high permittivity through a relatively simple process. However, the electromagnetic properties vary considerably, and the structure fabrication is complicated owing to the high viscosity. Additionally, it is challenging to analytically predict the electromagnetic properties of specimens before their permittivity can be measured. In this study, a high permittivity composite material was investigated, wherein the permittivity can be controlled and predicted analytically. Printed electronics were applied on the surface of glass fabric using a conductive paste to produce a micropattern printed fabric (MPF). The MPF was then studied to predict and control the permittivity of the composite material. In an MPF, conductive particles are distributed into micropatterns designed on the surface of glass fabric; therefore, uniform permittivity was obtained and could be controlled by moderating the parameters of micropatterns, such as pattern size and aspect ratio. The mechanical properties of the MPF were also investigated.

Laser heat-mode patterning with improved aspect-ratio

Heat-mode lithography has received much attention owing to its capacity of breaking through the diffraction limit and realizing nano-patterning. However, the relatively lower aspect ratio of patterns seriously limits its scope of applications. In the currently available literature, the aspect ratio of submicron structures prepared by this method is less than 0.3:1. In this work, a new two-step development process was proposed to considerably improve the aspect-ratio of micro/nanostructures in the AgInSbTe (AIST) heat-mode resist. An aspect ratio of 1:1 can be kept even for the grating structures with a linewidth/period of 200nm/400 nm. The developed patterns can be transferred to silicon substrates with high fidelity. This simple and effective technique addresses key issues of heat-mode lithography in the manufacture of functional nanostructures requiring high aspect ratio, such as photomasks, templets of nanoimprint, and so on.

Anisotropic and low damage III-V/Ge heterostructure etching for multijunction solar cell fabrication with passivated sidewalls

This article presents a complete plasma etching process to etch high aspect ratio patterns on III-V/Ge solar cell heterostructure with low damage for the fabrication of multijunction solar cells with a through cell via contact architecture. A SiCl 4 /H 2 chemistry was studied with different hydrogen dilutions within the plasma (0%, up to 67%) and with different cathode temperatures (20 ∘ C, up to 200 ∘ C). This chemistry choice creates a SiCl x -based inhibiting layer on the sidewalls that promotes anisotropic etching through the epitaxial heterostructure. The study suggests that a high hydrogen flow and a low temperature reduce the chemical reactions that create sidewall erosion. A high hydrogen flow appears to provide a hydrogen passivation of the non-radiative defects on the III-V heterostructure sidewall during the etching process. III-V/Ge triple junction solar cells with standard grid line and busbar front and back contacts have been fabricated and via-holes were plasma-etched through the active layers in order to investigate the impact of hydrogen passivation on the photovoltaic performance. The results demonstrate that the hydrogen passivation enables an open-circuit voltage increase that persists even after 5 months. This plasma process can also be used for the mesa etching step on multijunction solar cells with standard contacts. Thus, it could provide an appealing pathway to increase the conversion efficiency of state-of-the-art multijunction solar cells with standard contacts. To complete the etching process, a liner is used to protect the sidewall properties and a time-multiplexed Ge etching process is proposed to finalize the patterning and even open a pathway towards III-V/Ge plasma dicing. • A complete etching process is proposed to etch deep and anisotropic vias through a III-V/Ge heterostructure. • A low temperature SiCl 4 /H 2 plasma process is well suited to etch III-V/Ge heterostructures with limited sidewall erosion. • High H 2 flow enables a defect passivation on the etched sidewalls and it persists over several months.

Structural and Mechanical Properties of Silica Mesoporous Films Synthesized Using Deep X-Rays: Implications in the Construction of Devices

In recent years, the use of X-Rays (XR) irradiation for the production of ordered mesoporous thin films has been well established. This technique allows obtaining porous materials that contain thermal sensitive moieties or nanoparticles. Additionally, in combination with lithographic masks, the generation of high aspect ratio patterns of several geometrical shapes with micrometric resolution is possible. In this work, the structural and mechanical properties of porous silica thin films obtained by sol-gel method along with the exposure to high intensity XR is presented. Two templates (CTAB and Brij 58) and several irradiation doses and post-synthesis treatments were evaluated by a combination of characterization techniques, including grazing incidence small-angle XR scattering, electronic microscopies, XR reflectometry and nanoindentation. The results demonstrate that all the irradiated oxides presented a highly ordered mesoporous structure, independently of the XR dose and post thermal treatment. Their mechanical properties, on the other hand, clearly depend on the irradiation dose; high hardness values were measured on samples irradiated at low doses but higher doses are necessary to obtain films with indentation modulus values similar to the obtained for thermally treated coatings. The accessible porosity, essential for the application of these films in devices for micro- and nanofluidics, is also dependent on the dose and the thermal treatment performed afterward. The same tendency is observed for the films contraction and rigidity. After this characterization, it was concluded that thermal treatments are needed after the consolidation with XR to increase the accessibility and structural integrity of these porous oxides. Finally, the production of composites with metallic (Au and Ag) nanoparticles was tested which envisioned their applications in sensing and catalysis. Moreover, diverse geometrical patterns of both pure and Ag nanoparticles doped silica mesostructured films were obtained, demonstrating the feasibility of the proposed approach. The results presented in this work are of great importance to understand the transport mechanisms that operate in these silica porous films, in order to integrate them in different devices for lab-on-a-chip applications.

Etching Behaviors of Sapphire's C- Plane Cavity

Techniques to fabricate patterned sapphire substrates (PSSs) have attracted much attention in recent decades. Wet etching behaviors and crystalline sapphire processes are critical for PSSs applications to improve the performance of light-emitting diodes. This study investigated the shape evolution behaviors and associated kinetics of cavities on the c-{0001} plane in crystalline sapphire during wet etching. It was revealed that wet etching reduces the cavity aspect ratio, and the cavity shape is a complicated structure constructed by 15 faceted planes of c-{0001}, r-{11¯02}, p-{112¯3}, m-{101¯0}, and s-{11¯01} families. A constant etching rate was demonstrated, suggesting the step flow mechanism of etching. The etching activation energy of crystalline sapphire is reduced by preformation of cavities as elucidated by the Arrhenius kinetic model followed during the etching process. This study provides new insight into wet etching behaviors of crystalline sapphire and might open up a way for fabricating sapphire substrate with large aspect ratio patterns.